Means for intermediate modulation in television transmission



i 1940. J. SCHUNACK 2,2

MEANS FOR INTERMEDIATE MODULATION IN TELEVISION TRANSMISSION Filed Dec. ll,' 1936 Patented July 2, 1940 UNITED STATES MEANS FOR INTERIVIEDIATE MODULATION IN TELEVISION TRANSMISSION Johannes Schunack, Berlin-Oharlottenburg, Germany, assignor to the firm of Fernseh Aktiengesellschaft, Zehlendorf, near Berlin, Germany Application December 11, 1936, Serial No. 115,416 r In Germany December 23, 1935 3 Claims.

The invention relates to the transmission of television signals and deals more particularly with methods adapted for sending image and synchronizing signals over a common path, e. g., a cable or an ultra-short wave.

It is desirable in many cases to alter the transmission path and to interpose various types of transmission paths in sequential relation. For example, it may be desired to use a cable from the studio to the radio transmitter after which radio transmission is used, thereafter, another stretch of cable, and so on. The use of such circuits in sequential connected relation accompanied by repeated modulations causes difficulties at the modulated output terminii owing to distortion of the modulation curves.

These difliculties will be explained by way of an example. If, for example, a transmitting system is used, in which the synchronizing signal is produced by completely suppressing the carrier wave, where a 30% modulation corresponds to the black portions-of the image and a modulation of 100% to the white portions of the image, then, in the rectification, amplification and modulation, occurring at the ensuing fragmentary path these amplitude relationships will become altered. Since the modulation characteristic curve has an appreciable bend especially at its lower portion, the incoming modulation signal having an amplitude of about 30% in the new fragmentary path will amount to about 20% and this will no longer suflice for positively separating the synchronizing signals.

In accordance with the present invention, and to obviate these drawbacks, the synchronizing signal is filtered out at the intermediate station, is amplified per se, and is fed anew into the input of the next transmission stage.

The drawing illustrates an embodiment of the subject matter of the invention. Referring to the drawing:

Fig. 1 is a schematic representation of the transmission paths and intermediate stations.

Fig. 2 is a circuit according to the invention, and

Figs. 3-a and 3-b represent the modulation curves.

In Fig. 1 it is assumed that a cable 2 leads from transmitter l to the intermediate station 3. At this point radio transmission is used with the aid of transmitting antenna 4 and/or receiving antenna 5. Another intermediate station 6 follows, then a stretch of cable 1, and finally a receiver 8.

Fig. 2 shows the circuit of the intermediate station 3. The cable 2 leads to an amplifier 9 having two outputs. Output l0 leads to a rectifying tube ll through a transformer l2. The modulation voltages are taken off at a resistance l3 and fed to the radio transmitter I4 by modulating the ultra short waves. If only this path were to be utilized the radio signals would not receive the synchronizing impulses in sufiiciently modulated degree, if the transmission is elfected in the manner above described, since the bending of the modulation curve causes distortion of the amplitude relationships. This is shown in Figs. 3-a. and 3b, in which the straight line of Fig. 3a shows the amplitude distribution of the incoming signal and Fig. 3-1) the alteration of the amplitude values resulting from the bending of the characteristic curve.

Consequently a second rectifier tube I1 is interposed into the second output l5 of the amplifier 9 through a transformer It. The modulation voltage taken off at resistance It is fed to a tube l9 acting as .an amplitude filter, which filters out the synchronizing impulses. These synchronizing impulses are then, for example, amplified in an amplifier 20, and led to the input circuit of the radio transmitter I4. In this case it makes no difference where this supplementary signal is fed. It may, for example, be fed in to the preliminary stage or to the final modulation stage.

I claim:

1. In apparatus for the transmission through repeating stations of television signals involving combined image and synchronizing signals wherein the synchronizing signals represent an order of modulation which is not amplified to the same degree as the image signals, the method of preventing a change in the percentage of modulation of said synchronizing signals at a repeating station which comprises filtering out the synchronizing signals from the combined signal, amplifying the synchronizing signals separately and to a greater degree than said image signals and recombining the image and synchronizing components for modulation purposes at such repeating station.

2. In apparatus for the television transmission through a repeating station of signals involving combined image and wherein said synchronizing signals are of an order of modulation diifering from that of said image signals, the method of operation which comprises separating the image and synchronizing signals at such station, amplifying said synchronizing signals independently of and to a synchronizing signals.

difierent degree than said image signals, and which comprises amplifying the signals reprerecombining said signals for modulation pursenting one order of modulation, to a greater cle poses. gree than the signals representing another order 3. In a system for retransmitting combined of modulation, intermediate such demodulating image and synchronizing signals of different and modulating steps and modulating said differ 5 orders of modulation wherein a modulated carent carrier Wave With such amplified signal. rier wave is demodulated and a difierent carrier wave is subsequently modulated, the method JOHANNES SCHUNACK. 

